Well completion foamed spacer fluids and methods

ABSTRACT

Well completion foamed spacer fluids and methods of using the foamed spacer fluids are provided. A method of the invention for displacing a first fluid from a well bore with an incompatible second fluid comprises the following steps. A foamed spacer fluid is placed between the first and second fluids to separate the first and second fluids and to remove the first fluid from the walls of the well bore. Thereafter, the first fluid and the foamed spacer fluid are displaced from the well bore with the second fluid.

CROSS-REFERENCE TO RELATED APPLICATION

This Application is a Divisional of Ser. No. 10/393,965, filed Mar. 21,2003, now U.S. Pat. No. 6,668,927.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to foamed spacer fluids and methods ofusing the spacer fluids in well completions such as primary cementing.

2. Description of the Prior Art

Well bores are commonly drilled using the rotary drilling method. Inthat method, a drill bit connected to a drill string is rotated whiledrilling fluid is circulated through the drill string, through the drillbit and upwardly to the surface through the annulus between the drillstring and the walls of the well bore being drilled. The drilling fluidfunctions to cool the drill bit, to remove cuttings from the well boreand to maintain hydrostatic pressure on the well bore. The hydrostaticpressure prevents formation fluids from entering the well bore duringdrilling.

The drilling fluid also forms a filter cake on the walls of the wellbore which prevents the drilling fluid from being lost into permeablesubterranean zones. However, the drilling fluid in the filter cakedehydrates and gels thereby forming a layer of solids and gelleddrilling fluid on the walls of the well bore. While this filter cake isadvantageous during drilling, it is detrimental to obtaining effectivedrilling fluid displacement and removal from the walls of the well bore.

In primary well cementing operations, a hydraulic cement slurry ispumped into the annular space between the walls of the well bore and theexterior surfaces of a pipe string disposed therein. The cement slurryis allowed to set in the annular space thereby forming an annular sheathof hardened substantially impermeable cement therein. The cement sheathphysically supports and positions the pipe in the well bore and bondsthe exterior surfaces of the pipe to the walls of the well bore wherebythe undesirable migration of fluids between zones or formationspenetrated by the well bore is prevented. If the drilling fluid filtercake is not adequately removed from the walls of the well bore orportions thereof, a competent seal between the hardened cement and thewell bore does not result.

Spacer fluids are typically placed between two fluids contained or to bepumped within well bores. Examples of fluids between which spacer fluidsare utilized include between hydraulic cement slurries and drillingfluids, between different drilling fluids during drilling fluidchangeouts and between drilling fluids and completion brines. Thespacers are also utilized to enhance drilling fluid and filter cakeremoval from the walls of well bores, to enhance displacement efficiencyand to physically separate chemically incompatible fluids. For example,a hydraulic cement slurry and drilling fluid are separated by a spacerfluid when the cement slurry is placed in the annulus between a pipestring and the walls of a well bore. The spacer fluid preventsintermixing of the cement slurry and the drilling fluid and facilitatesthe removal of filter cake and gelled drilling fluid from the walls ofthe well bore during displacement of the drilling fluid by the cementslurry. If intermixing of the cement slurry and the drilling fluidoccurs, viscous masses are formed in the annulus that prevent continueddisplacement.

The heretofore utilized spacer fluids have achieved varying degrees ofsuccess in displacing fluids and removing filter cake, gelled drillingfluid and the like from the walls of the well bore. However, there is acontinuing need for improved spacer fluids that achieve greater removalof drilling fluid and filter cake from the walls of the well bore andprevent mixing of incompatible fluids.

SUMMARY OF THE INVENTION

The present invention provides improved water based well completionfoamed spacer fluids and methods of using the foamed spacer fluids whichmeet the need described above and overcome the deficiencies of the priorart. The foamed spacer fluids of this invention exhibit better drillingfluid and drilling fluid filter cake removal because the gas in thefoamed spacer fluids energizes the fluids. The gas bubbles arecompressed as a foamed spacer fluid is pumped down the pipe string andthe hydrostatic pressure increases. As the foamed spacer fluid entersthe annulus and is pumped toward the surface, the hydrostatic pressuredecreases which allows the gas bubbles to expand and cause the foamedspacer fluid to achieve highly efficient drilling fluid removal from theannulus. The expansion of the gas bubbles also allows the foamed spacerfluid to enter irregular hole configurations and enlarged holes in thewell bore and remove drilling fluid and filter cake therefrom. Finally,the increased viscosity of a foamed spacer fluid provides bettersuspension of removed drilling fluid than the heretofore utilized spacerfluids. The water-based foamed spacer fluids of this invention areparticularly well suited for displacing water-based drilling fluids andother water-based fluids.

The water-based foamed spacer fluids are comprised of water, a weightingmaterial, a dispersing agent, a suspending agent and friction reducer, amixture of foaming and foam stabilizing surfactants and a gas.

The methods are comprised of the following steps. A foamed spacer fluidis placed between first and second fluids in a well bore to separate thefirst and second fluids and to remove the first fluid from the walls ofthe well bore. Thereafter, the first fluid and the foamed spacer fluidare displaced from the well bore by the second fluid.

The objects, features and advantages of the present invention will bereadily apparent to those skilled in the art upon a reading of thedescription of preferred embodiments which follows.

DESCRIPTION OF PREFERRED EMBODIMENTS

The water-based foamed spacer fluids of this invention are basicallycomprised of water, a weighting material, a dispersing agent, asuspending agent and friction reducer, a mixture of foaming and foamstabilizing surfactants and a gas.

A method of this invention for displacing a first fluid from a well borewith an incompatible second fluid is comprised of the following steps. Afoamed spacer fluid is placed between the first and second fluids toseparate the first and second fluids and to remove the first fluid fromthe walls of the well bore. Thereafter, the first fluid and the foamedspacer fluid are displaced from the well bore by the second fluid. Thefoamed spacer fluid of this invention is particularly suitable for usebetween a drilling fluid and a hydraulic cement slurry.

The water in the foamed spacer fluids of this invention can be freshwater or salt water. The term “salt water” is used herein to meanunsaturated salt solutions and saturated salt solutions including brinesand seawater.

Examples of weighting materials that can be utilized in the foamedspacer fluid include, but are not limited to, barium sulfate, hematite,manganese tetraoxide and calcium carbonate. Of these, barium sulfate ispreferred. The weighting material is included in the foamed spacerfluids in an amount in the range of from about 49 to about 576 poundsper barrel of water therein.

The dispersing agent is included in the foamed spacer fluids to dispersethe solids and other materials in the water. Examples of dispersingagents that can be utilized include, but are not limited to, naphthalenesulfonate condensed with formaldehyde, sodium polyacrylate, a terpolymerof acrylic acid, alkyloxybenzene sulfonate and methally sulfonate,formaldehyde, acetone, bisulfate condensate, melamine formaldehydecondensate, and mixtures thereof. The dispersing agent is included inthe foamed spacer fluid in an amount in the range of from about 3.5% toabout 6% by weight of the water therein.

The suspending agent and friction reducer is included in the foamedspacer fluid to suspend the weighting material and other solids thereinas well as to reduce friction during pumping of the foamed spacer fluid.Examples of suspending agent and friction reducers that can be utilizedinclude, but are not limited to, sepiolite, whelan gum, xanthan gum,hydroxyethylcellulose, bentonite, attapulgite, and mixtures thereof. Ofthese, xanthan gum is preferred. The suspending agent and frictionreducer is included in the foamed spacer fluid in an amount in the rangeof from about 0.5% to about 2.0% by weight of water therein.

The mixture of foaming and foam stabilizing surfactants functions tofacilitate the formation of a foam and to stabilize the foam during itsuse. Examples of such surfactant mixtures that can be used include, butare not limited to, a mixture of an ethoxylated alcohol ether sulfatesurfactant, an alkyl or alkene amidopropyl betaine surfactant and analkyl or alkene admidopropyl dimethyl amine oxide surfactant and amixture of an alpha-olefinic sulfonate surfactant and an alkyl or alkeneamidopropyl betaine surfactant. Of these, the mixture of an ethoxylatedalcohol ether sulfate surfactant, an alkyl or alkene amidopropyl betainesurfactant and an alkyl or alkene admidopropyl dimethyl amine oxidesurfactant is preferred. This mixture is described in detail in U.S.Pat. No. 6,063,738 issued to Chatterji, et al. on May 16, 2000, which isincorporated herein by reference thereto. The mixture of foaming andfoam stabilizing surfactants is included in the spacer fluid in anamount in the range of from about 0.5% to about 5% by weight of thewater therein.

The gas in the foamed spacer fluid is preferably nitrogen. Generally,the gas is present in the foamed spacer fluid in an amount in the rangeof from about 15% to about 70% by volume of the water therein.

The foamed spacer fluid can optionally include a well bore scouringmaterial to facilitate the removal of filter cake and gelled drillingfluid from the walls of the well bore. Examples of suitable scouringmaterials include, but are not limited to, diatomaceous earth,crystalline silica, amorphous silica, and mixtures thereof. Of these,crystalline silica scouring material is preferred. When used, thescouring material is present in the foamed spacer fluid in an amount inthe range of from about 15% to about 30% by weight of the water therein.

As mentioned above, the foamed spacer fluids of this invention areparticularly useful in primary cementing operations wherein the foamedspacer fluid is placed between a drilling fluid and a hydraulic cementslurry. The drilling fluid can be a water-based drilling fluid, or afoamed drilling fluid.

The hydraulic cement slurry can include various cements includingPortland cements, slag cements, pozzolana cements, gypsum cements,aluminous cements, silica cements or high alkalinity cements. Of these,Portland cement is generally preferred. The water in the hydrauliccement slurry can be fresh water or salt water.

A preferred method of this invention for displacing a first fluid from awell bore with an incompatible second fluid comprises the steps of: (a)placing a foamed spacer fluid between the first and second fluids toseparate the first and second fluids and to remove the first fluid fromthe walls of the well bore; and then (b) displacing the first fluid andthe foamed spacer fluid from the well bore with the second fluid.

A preferred method of displacing drilling fluid from a well bore with ahydraulic cement slurry comprises the steps of: (a) placing a foamedspacer fluid between the drilling fluid and the hydraulic cement slurryto separate the drilling fluid from the hydraulic cement slurry and toremove the drilling fluid and filter cake from the walls of the wellbore, the foamed spacer fluid being comprised of water, a weightingmaterial, a dispersing agent, a suspending agent and friction reducer, ascouring agent, a mixture of foaming and foam stabilizing surfactantsand a gas; and then (b) displacing the drilling fluid and the foamedspacer fluid from the well bore with the hydraulic cement slurry.

A preferred foamed spacer fluid of this invention comprises: water; aweighting material; a dispersing agent; a suspending agent and frictionreducer; a mixture of foaming and foam stabilizing surfactant; and agas.

In order to further illustrate the methods and foamed spacer fluids ofthis invention, the following examples are given.

EXAMPLE 1

A first spacer fluid having a density of 16 pounds per gallon wasprepared comprised of 240 grams of fresh water, 397 grams of bariumsulfate weighting material, 3.43 grams of a dispersant comprisingnaphthalene sulfonate condensed with formaldehyde, 4.12 grams ofsepiolite suspending agent and friction reducer, 13.73 grams ofdiatomaceous earth scouring material, 12.25 grams of crystalline silicascouring material, 4.8 grams of a mixture of foaming and foamstabilizing surfactants comprised of an ethoxylated alcohol ethersulfate surfactant, an alkyl or alkene amidopropyl betaine surfactantand an alkyl or alkene amidopropyl dimethyl amine oxide surfactant, and0.69 grams of a defoaming agent comprising oil and silica. Equalportions of the spacer fluid were then foamed with air to form foamedspacer fluids having densities of 10 pounds per gallon, 12 pounds pergallon and 14 pounds per gallon. Each of the portions of the foamedspacer fluid were then tested for rheology. The results of these testsare given in Table I below.

Three non-foamed spacer fluids were prepared having densities of 10pounds per gallon, 12 pounds per gallon and 14 pounds per gallon,respectively. The 10 pound per gallon non-foamed spacer fluid wascomprised of 309.7 grams of fresh water, 45 grams of barium sulfateweighting material, 6.37 grams of a naphthalene sulfonate condensed withformaldehyde dispersing agent, 7.64 grams of sepiolite suspending agentand friction reducer, 25.4 grams of diatomaceous earth scouringmaterial, 22.75 grams of crystalline sand scouring material, 6.19 gramsof the mixture of foaming and foam stabilizing surfactants describedabove and 1.27 grams of oil and silica defoamer. 0.74 cubic centimetersof a spacer mixing aid was added to the 10 pound per gallon non-foamedspacer fluid and the resulting mixture was blended. The spacer mixingaid had the following composition: 39.5% xanthan gum, 48.3% mineral oil,2.70% oleophilic clay, 5.9% nonylphenol with 3 moles of ethyleneoxideand 3.9% naphthalene sulfonate condensed with formaldehyde.

The 12 pound per gallon non-foamed spacer fluid was comprised of 286.5grams of fresh water, 163 grams of barium sulfate weighting material,5.39 grams of the dispersing agent described above, 6.47 grams of thesuspending agent and friction reducer described above, 21.58 grams ofdiatomaceous earth scouring material, 19.25 grams of crystalline sandscouring material, 5.72 grams of the mixture of foaming and foamstabilizing surfactants described above, and 1.08 grams of the defoamingagent described above. In addition, 0.68 cubic centimeters of the spacermixing aid described above was added to the spacer fluid. Thereafter,the non-foamed spacer fluid was blended.

The 14 pound per gallon non-foamed spacer fluid comprised 263 grams offresh water, 280 grams of barium sulfate weighting material, 4.41 gramsof the dispersing agent described above, 5.92 grams of the suspendingagent and friction reducer described above, 17.65 grams of thediatomaceous earth scouring material, 15.75 grams of the crystallinesand scouring material, 5.26 grams of the mixture of foaming and foamstabilizing surfactants, 0.88 grams of the oil and silica defoamingagent and 0.63 cubic centimeters of the above described spacer mixingaid. Thereafter, the non-foamed spacer fluid was blended.

The rheologies of the non-foamed spacer fluids described above weremeasured and are set forth in Table II below.

TABLE I Foamed Spacer Fluid Rheologies At 80° F., 130° F. and 180° F. 10lb/gal 12 lb/gal 14 lb/gal Foamed Spacer Foamed Spacer Foamed Spacer RPM80° F. 130° F. 180° F. 80° F. 130° F. 180° F. 80° F. 130° F. 180° F. 60095 54 40 62 20 20 38 33 30 300 58 41 30 40 14 11 20 19 19 200 43 38 2230 11 7 14 14 15 100 30 32 19 21 8 5 9 9 11 6 17 23 12 13 6.5 4 2.5 5 73 17 22 11 12 6.5 3.5 2.5 5 7

TABLE II Non-Foamed Spacer Fluid Rheologies At 80° F., 130° F. and 180°F. 10 lb/gal 12 lb/gal 14 lb/gal Non-Foamed Spacer Non-Foamed SpacerNon-Foamed Spacer RPM 80° F. 130° F. 180° F. 80° F. 130° F. 180° F. 80°F. 130° F. 180° F. 600 17 13 12.5 32 25 33 50 45 57 300 10 8 8 19 16 2330 30 35 200 7 6 6.5 15 12 19 22 25 26 100 5 4.5 5 10 9.5 15 15 19 18 62 3 4.5 6 8 13 6.5 7 8 3 2 3 4.5 6 8 13 6.5 7 7

From Tables I and II, it can be seen that the rheologies of the foamedspacer fluids of this invention are much higher than the rheologies ofthe non-foamed spacer fluids at temperatures of 80° F., 130° F. and 180°F. The higher rheologies of the foamed spacer fluids of this inventionallow them to be pumped in laminar flow at reasonable displacementrates. These properties improve drilling fluid displacement whilemaintaining drilling fluid and cement slurry isolation.

EXAMPLE 2

The procedures and tests described above were repeated except that thefoamed and non-foamed spacer fluids tested were different from thosedescribed in Example 1. That is, a 16 pound per gallon mixture wasprepared comprising 244.4 grams of water, 407.4 grams of barium sulfateweighting material, 1.16 grams of sodium polyacrylate dispersing agent,0.73 grams of an acrylic acid, alkyloxybenzene sulfonate and methallysulfonate terpolymer dispersant, 0.29 grams of whelan gum suspendingagent and friction reducer, 0.1 gram of hydroxyethylcellulose suspendingagent and friction reducer, 4.34 grams of sepiolite suspending agent andfriction reducer, 12.74 grams of amorphous silica scouring material and4.8 grams of the mixture of foaming and foam stabilizing surfactantsdescribed above.

The 16 pound per gallon spacer composition was divided into threeportions. The first portion was foamed with air to a density of 10pounds per gallon, the second portion was foamed with air to a densityof 12 pounds per gallon and the third portion was foamed with air to adensity of 14 pounds per gallon. Each of the foamed portions were thentested for rheology at 80° F., 130° F. and 180° F. The results of thesetests are set forth in Table III below.

A 10 pound per gallon non-foamed spacer fluid was prepared comprised of318.4 grams of fresh water, 64.8 grams of barium sulfate weightingmaterial, 2.17 grams of sodium polyacrylate dispersing agent, 1.38 gramsof an acrylic acid, alkyloxybenzene sulfonate and methally sulfonateterpolymer dispersant, 0.54 grams of whelan gum suspending agent andfriction reducer, 0.18 grams of hydroxyethylcellulose suspending agentand friction reducer, 8.15 grams of sepiolite suspending agent andfriction reducer and 23.89 grams of amorphous silica scouring material.

The 12 pound per gallon non-foamed spacer comprised 293.7 grams of freshwater, 179 grams of barium sulfate weighting agent, 1.84 grams of sodiumpolyacrylate dispersing agent, 1.6 grams of the above describedterpolymer dispersing agent, 0.46 grams of whelan gum suspending agentand friction reducer, 0.15 grams of hydroxyethylcellulose suspendingagent and friction reducer, 6.89 grams of sepiolite suspending agent andfriction reducer and 20.2 grams of amorphous silica scouring material.

The 14 pound per gallon non-foamed spacer comprised 269.1 grams of freshwater, 293.2 grams of barium sulfate weighting material, 1.49 grams ofsodium polyacrylate dispersant, 0.95 grams of the above describedterpolymer dispersant, 0.37 grams of whelan gum suspending agent andfriction reducer, 0.12 grams of hydroxyethylcellulose suspending agentand friction reducer, 5.6 grams of sepiolite dispersing agent andfriction reducer and 16.43 grams of amorphous silica scouring agent.After being prepared, the non-foamed spacing fluids were blended. Afterbeing blended, the non-foamed spacer fluids were each tested forrheology at 80° F., 130° F. and 180° F. The results of these tests areset forth in Table IV below.

TABLE III Foamed Spacer Fluid Rheologies At 80° F., 130° F. and 180° F.10 lb/gal 12 lb/gal 14 lb/gal Foamed Spacer Foamed Spacer Foamed SpacerRPM 80° F. 130° F. 180° F. 80° F. 130° F. 180° F. 80° F. 130° F. 180° F.600 174 90 57 150 88 50 127 88 69 300 117 59 38 100 57 35 85 59 46 20092 46 30 79 45 29 67 46 37 100 63 31 22 55 31 21 47 32 25 6 19 8 6 16 96.5 15 10 7 3 15 6.5 4 13 6.5 5 12 7.5 5

TABLE IV Non-Foamed Spacer Fluid Rheologies At 80° F., 130° F. and 180°F. 10 lb/gal 12 lb/gal 14 lb/gal Non-Foamed Spacer Non-Foamed SpacerNon-Foamed Spacer RPM 80° F. 130° F. 180° F. 80° F. 130° F. 180° F. 80°F. 130° F. 180° F. 600 49 37 32 82 60 51 97 72 61 300 36 28 25 60 47 3968 51 44 200 31 25 22 47 42 34 55 42 36 100 24 20 17.5 36 31 26 41 31 276 9 8 7.5 14 12 10 17 12.5 10 3 7.5 6.5 6 11 10 8 14 10.5 8

From Tables III and IV above, it can been seen that the foamed spacerfluids of this invention have higher rheologies than the non-foamedspacer fluids. The higher rheologies of the foamed spacer fluids allowthem to be pumped in laminar flow at reasonable displacement rates.These properties improve drilling fluid and filter cake removal from thewalls of the well bore while maintaining drilling fluid and cementslurry isolation.

1. A foamed spacer fluid comprising: water selected from the groupconsisting of fresh water and salt water; a weighting material selectedfrom the group consisting of barium sulfate, hematite, manganesetetraoxide and calcium carbonate present in an amount in the range offrom about 49 to about 576 pounds per barrel of water; a dispersingagent selected from the group consisting of naphthalene sulfonatecondensed with formaldehyde; sodium polyacrylate, a terpolymer ofacrylic acid, alkyloxybenzene sulfonate and methally sulfonate,formaldehyde, acetone, bisulfate condensate, melamine formaldehydecondensate, and mixtures thereof; a suspending agent and frictionreducer; a mixture of foaming and foam stabilizing surfactants; and agas.
 2. The foamed spacer fluid of claim 1 wherein the dispersing agentis present in the foamed spacer fluid in an amount in the range of fromabout 3.5% to about 6% by weight of the water therein.
 3. The foamedspacer fluid of claim 1 wherein the suspending agent and frictionreducer is selected from the group consisting of sepiolite, whelan gum,xanthan gum, hydroxyethyl cellulose, bentonite, attapulgite, andmixtures thereof.
 4. The foamed spacer fluid of claim 1 wherein thesuspending agent and friction reducer is xanthan gum.
 5. The foamedspacer fluid of claim 1 wherein the suspending agent and frictionreducer is present in the foamed spacer fluid in an amount in the rangeof from about 0.5% to about 2% by weight of the water therein.
 6. Thefoamed spacer fluid of claim 1 wherein the mixture of foaming and foamstabilizing surfactants is selected from the group consisting of amixture of an ethoxylated alcohol ether sulfate surfactant, an alkyl oralkene amidopropyl betaine surfactant and an alkyl or alkene amidopropyldimethyl amine oxide surfactant and a mixture of an alpha-olefinicsulfonate surfactant and an alkyl or alkene amidopropyl betainesurfactant.
 7. The foamed spacer fluid of claim 1 wherein the mixture offoaming and foam stabilizing surfactants is a mixture of an ethoxylatedalcohol ether sulfate surfactant, an alkyl or alkene amidopropyl betainesurfactant and an alkyl or alkene amidopropyl dimethyl amine oxidesurfactant.
 8. The foamed spacer fluid of claim 1 wherein the mixture offoaming and foam stabilizing surfactants is present in the foamed spacerfluid in an amount in the range of from about 0.5% to about 5% by weightof the water therein.
 9. The foamed spacer fluid of claim 1 wherein thegas is nitrogen.
 10. The foamed spacer fluid of claim 1 wherein the gasis present in the foamed spacer fluid in an amount in the range of fromabout 15% to about 70% by volume of the water.
 11. The foamed spacerfluid of claim 1 which further comprises a well bore wall scouringmaterial selected from the group consisting of diatomaceous earth,crystalline silica, amorphous silica, and mixtures thereof.
 12. Thefoamed spacer fluid of claim 11 wherein the scouring material iscrystalline silica.
 13. The foamed spacer fluid of claim 11 wherein thescouring material is present in the foamed spacer fluid in an amount inthe range of from about 15% to about 30% by weight of the water therein.14. A foamed spacer fluid comprising: water; a weighting materialselected from the group consisting of barium sulfate, hematite,manganese tetraoxide and calcium carbonate; a dispersing agent selectedfrom the group consisting of naphthalene sulfonate condensed withformaldehyde, sodium polyacrylate, a terpolymer of acrylic acid,alkyloxybenzene sulfonate and methally sulfonate, formaldehyde, acetone,bisulfate condensate, melamine formaldehyde condensate, and mixturesthereof; a suspending agent and friction reducer selected from the groupconsisting of sepiolite, whelan gum, xanthan gum, hydroxyethylcellulose, bentonite, attapulgite, and mixtures thereof; a mixture offoaming and foam stabilizing surfactants selected from the groupconsisting of a mixture of an ethoxylated alcohol ether sulfatesurfactant, an alkyl or alkene amidopropyl betaine surfactant and analkyl or alkene amidopropyl dimethyl amine oxide surfactant and amixture of an alpha-olefinic sulfonate surfactant and an alkyl or alkeneamidopropyl betaine surfactant; and a gas.
 15. The foamed spacer fluidof claim 14 wherein the water is selected from the group consisting offresh water and salt water.
 16. The foamed spacer fluid of claim 14wherein the weighting material is barium sulfate.
 17. The foamed spacerfluid of claim 14 wherein the weighting material is present in an amountin the range of from about 49 to about 576 pounds per barrel of water inthe spacer fluid.
 18. The foamed spacer fluid of claim 14 wherein thedispersing agent is present in the foamed spacer fluid in an amount inthe range of from about 3.5% to about 6% by weight of the water therein.19. The foamed spacer fluid of claim 14 wherein the suspending agent andfriction reducer is xanthan gum.
 20. The foamed spacer fluid of claim 14wherein the suspending agent and friction reducer is present in thefoamed spacer fluid in an amount in the range of from about 0.5% toabout 2% by weight of the water therein.
 21. The foamed spacer fluid ofclaim 14 wherein the mixture of foaming and foam stabilizing surfactantsis a mixture of an ethoxylated alcohol ether sulfate surfactant, analkyl or alkene amidopropyl betaine surfactant and an alkyl or alkeneamidopropyl dimethyl amine oxide surfactant.
 22. The foamed spacer fluidof claim 14 wherein the mixture of foaming and foam stabilizingsurfactants is present in the foamed spacer fluid in an amount in therange of from about 0.5% to about 5% by weight of the water therein. 23.The foamed spacer fluid of claim 14 wherein the gas is nitrogen.
 24. Thefoamed spacer fluid of claim 14 wherein the gas is present in the foamedspacer fluid in an amount in the range of from about 15% to about 70% byvolume of the water.
 25. The foamed spacer fluid of claim 14 whichfurther comprises a well bore wall scouring material selected from thegroup consisting of diatomaceous earth, crystalline silica, amorphoussilica, and mixtures thereof.
 26. The foamed spacer fluid of claim 25wherein the scouring material is crystalline silica.
 27. The foamedspacer fluid of claim 25 wherein the scouring material is present in thefoamed spacer fluid in an amount in the range of from about 15% to about30% by weight of the water therein.
 28. A foamed spacer fluidcomprising: water selected from the group consisting of fresh water andsalt water; a weighting material selected from the group consisting ofbarium sulfate, hemitate, manganese tetraoxide and calcium carbonatepresent in an amount in the range of from about 49 to about 576 poundsper barrel of water in the spacer fluid; a dispersing agent selectedfrom the group consisting of naphthalene sulfonate condensed withformaldehyde, sodium polyacrylate, a terpolymer of acrylic acid,alkyloxybenzene sulfonate and methally sulfonate, formaldehyde, acetone,bisulfate condensate, melamine formaldehyde condensate, and mixturesthereof present in an amount in the range of from about 3.5% to about 6%by weight of water in the spacer fluid; a suspending agent and frictionreducer present in an amount in the range of from about 0.5% to about 5%by weight of water in the spacer fluid; a mixture of foaming and foamstabilizing surfactants present in an amount in the range of from about0.5% to about 5% by weight of water in the spacer fluid; and a gaspresent in an amount in the range of from about 15% to about 70% byvolume of water in the spacer fluid.
 29. The foamed spacer fluid ofclaim 28 wherein the suspending agent and friction reducer is selectedfrom the group consisting of sepiolite, whelan gum, xanthan gum,hydroxyethyl cellulose, bentonite, attapulgite, and mixtures thereof.30. The foamed spacer fluid of claim 28 wherein the suspending agent andfriction reducer is xanthan gum.
 31. The foamed spacer fluid of claim 28wherein the mixture of foaming and foam stabilizing surfactants isselected from the group consisting of a mixture of an ethoxylatedalcohol ether sulfate surfactant, an alkyl or alkene amidopropyl betainesurfactant and an alkyl or alkene amidopropyl dimethyl amine oxidesurfactant and a mixture of an alpha-olefinic sulfonate surfactant andan alkyl or alkene amidopropyl betaine surfactant.
 32. The foamed spacerfluid of claim 28 wherein the mixture of foaming and foam stabilizingsurfactants is a mixture of an ethoxylated alcohol ether sulfatesurfactant, an alkyl or alkene amidopropyl betaine surfactant and analkyl or alkene amidopropyl dimethyl amine oxide surfactant.
 33. Thefoamed spacer fluid of claim 28 wherein the gas is nitrogen.
 34. Thefoamed spacer fluid of claim 28 which further comprises a well bore wallscouring material selected from the group consisting of diatomaceousearth, crystalline silica, amorphous silica, and mixtures thereof. 35.The foamed spacer fluid of claim 34 wherein the scouring material iscrystalline silica.
 36. The foamed spacer fluid of claim 34 wherein thescouring material is present in the foamed spacer fluid in an amount inthe range of from about 15% to about 30% by weight of the water therein.